BIODIVERSITY
Sorting out venom versus poison.
Last issue we committed the cardinal science sin of using the word “poisonous” when we meant “venomous” - it was in the context of a diving water spider. Thanks to those readers who quite rightly pointed out that a toxin that is injected by an animal to subdue prey or defend against an attack, is indeed venom. Poison is a toxin grown in the animal, that kills or sickens, if that animal is itself eaten.
Venom also often differs from poison in that if it is ingested, stomach acid breaks down the chemicals in the venom and the person idiot who drank the venom won’t be affected. Of course, we don’t advise drinking venom, because this rule is not hard and fast, and if you have any tears or cuts or nicks any place where the venom can get into your bloodstream on the way to your stomach, well, you’re in trouble.
As we reflected on our venom/poison error, however, we began to wonder. Is there an animal that, because of the chemical nature of its venom, is also technically poisonous too?
And here’s an example: Australia’s own blue-ringed octopus. There are actually four species, one of which is called the blue-lined octopus, and one of which ( H. nierstraszi) has only been seen twice by scientists: once in 1938 and not again until 2013.
Of the three that are well-known, all can be found in Australian waters. And as all good Australians know, getting bitten by a blue-ringed octopus is deadly.
Their saliva is full of what’s called tetrodotoxin (or TTX). This nasty substance doesn’t kill you, it just paralyses you. Sadly for you, one of the bits it paralyses is your diaphragm, so you end up suffocating. Onset of this can take as little as five minutes. Yet despite the lack of antivenom, if a victim is placed on an artificial respirator for 24 hours, the toxin wears off.
Fortunately for humans, these little cephalopods aren’t aggressive, and normally try their best to first escape, and then warn you off with their bright blue rings. This may be why only two people in Australia (on record) have died from Hapalochlaena bites.
So where does the poison come into it? When scientists first started examining the blue-ringed octopus (working in pairs, both trained in CPR), they discovered the venom came from the animal’s salivary glands.
The octopus doesn’t make the venom itself, rather it cultivates a specific bacteria that generates the TTX. At first, biologists called this chemical “maculotoxin”, and realised it was very similar to the toxin found in some puffer-fishes (see above).
Later experiments determined that in fact maculotoxin is TTX, and that many fish, harlequin frogs, Californian newts, and a grab-bag of sea critters from squirts to crabs, all use the same stuff.
Many of these animals are not “venomous” because they don’t inject the toxin. But it’s the same chemical. TTX does affect you if you drink it, and this means the blue-ringed octopus is both venomous
and poisonous. If one refuses to bite you, biting it will get you just as dead.